<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>

</body>
<script>
  var arr = [1, 2, 3, 4];
  arr[4] = 5;
  arr[6] = 7;

  console.log(arr);

</script>
</html>